Optical device of a refractive optical element combined with a metasurface configuration

Abstract

The application provides an optical device with a refractive optical element and a metasurface composite configuration, the optical device being composed of a refractive optical element and a metasurface in cascade, the phase distribution of the refractive optical element at at least one wavelength in a target working waveband satisfying the imaging requirement of the optical device, and the phase distribution of the metasurface correcting the chromatic aberration of the refractive optical element in the target working waveband, so that the phase distribution of electromagnetic waves at different wavelengths in the target working waveband after passing through the optical device satisfies the imaging requirement of the optical device at the same time. The optical device integrates the refractive optical element and the metasurface in cascade, thereby meeting the light weight and integration requirements of an optical system, breaking through the bottleneck of mutual restriction between an aperture and a bandwidth, and meeting the aperture and bandwidth requirements in actual applications.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of micro-nano optical devices, optical imaging, and the like, and is an optical device with a refractive optical element and a metasurface composite configuration. BACKGROUND

[0002] Optical imaging plays an important role in national economy and national defense science and technology. The key to realizing high-quality optical imaging is an optical system. In the current optical system, a traditional refractive lens is used, and the phase control is established on the basis of geometric optics, which is often large in volume and weight. In addition, in order to optimize the imaging quality of the optical system, a complex lens group composed of multiple lenses is often used to correct chromatic aberration, which further increases the volume and weight of the optical system. Due to the fundamental limitation of the phase control principle of the traditional refractive lens, it cannot meet the development requirements of light weight and integration of the optical system.

[0003] A metasurface is a new type of artificial micro-nano structure, which is a two-dimensional array composed of optical scattering structures with a subwavelength feature size. The metasurface has the advantages of easy integration of planar configuration, high design freedom, and flexible control of amplitude, phase, and polarization.

[0004] It has been proposed to use a metasurface to realize the function of a lens. However, due to the limitation of the micro-nano processing technology, the size parameters of the optical scattering structures of the metasurface are limited, which makes the focusing and imaging effect of a single metasurface lens restricted by the aperture and bandwidth. Under the limitation of micro-nano processing technology, when the bandwidth of the metasurface lens (hundred nm to mu m level) covers the required working wavelength, the aperture can only reach the hundred mu m level, which cannot meet the requirements of the optical system for the aperture of the metasurface lens in practical applications; and when the aperture of the metasurface lens reaches the mm to cm level required by the application, the bandwidth can only reach the nm to 10 nm level, which cannot meet the demand of the optical system for the bandwidth in practical applications.

[0005] Therefore, it is necessary to provide an optical device with a refractive optical element and a metasurface composite configuration to meet the requirements of light weight and integration of the optical system, and to break through the bottleneck of mutual restriction of aperture and bandwidth. SUMMARY

[0006] The purpose of the present application is to provide an optical device with a refractive optical element and a metasurface composite configuration to meet the requirements of light weight and integration of the optical system, and to break through the bottleneck of mutual restriction of aperture and bandwidth.

[0007] In order to achieve the above-mentioned purpose, the application provides a refractive optical element and metasurface composite configuration optical device, characterized in that the refractive optical element and metasurface composite configuration optical device is composed of a refractive optical element and a metasurface, the phase distribution of the refractive optical element at at least one wavelength in the target working waveband meets the imaging requirements of the optical device, and the phase distribution of the metasurface is set to correct the chromatic aberration of the refractive optical element in the target working waveband, so that the phase distribution of the electromagnetic wave at different wavelengths in the target working waveband after passing through the optical device meets the imaging requirements of the optical device at the same time.

[0008] The metasurface is composed of a substrate and a micro-nano structure, the micro-nano structure is composed of a periodic array of two-dimensionally arranged micro-nano structure units, the micro-nano structure units have variable pointing angles, the pointing angles of different micro-nano structure units are different, and the remaining geometric parameters are the same; the pointing angle of each micro-nano structure unit is determined according to the required phase regulation amount of the electromagnetic wave passing through each micro-nano structure unit and the corresponding relationship between the phase regulation amount of the electromagnetic wave passing through the micro-nano structure unit and the pointing angle of the micro-nano structure unit; the phase regulation amount of the electromagnetic wave passing through each micro-nano structure unit meets the phase distribution of the metasurface.

[0009] The periodic array is a square lattice array or a hexagonal lattice array, the period U of the periodic array is 0.2λ to λ, and the micro-nano structure unit is an elliptical cylinder or a rectangular column, λ is a specified wavelength in the target working waveband.

[0010] The pointing angle of the micro-nano structure unit is between 0 and π, and the height H of the micro-nano structure unit is 0.5λ to 1.5λ.

[0011] The micro-nano structure unit is a rectangular column, the rectangular long side L and the rectangular short side W are 0.1U to 0.9U, and U is the period of the periodic array.

[0012] One side of the refractive optical element is a plane, and the other side is a curved surface, the curved surface of the refractive optical element faces the propagation direction of the incident light, and the plane faces away from the propagation direction of the incident light, and the metasurface is closely attached to the plane of the refractive optical element through the substrate thereof.

[0013] The refractive optical element has a focusing function, and the ratio of the metasurface to the aperture of the refractive optical element is 0.7-0.99.

[0014] The refractive optical element adopts a plano-convex mirror configuration, and the imaging requirement of the optical device means that the refractive optical element focuses to a focal plane with a preset focal length.

[0015] The phase distribution of the metasurface is:

[0016]

[0017] wherein B is a second Cauchy dispersion coefficient, λ0 is a center wavelength of a target working wavelength band, R is a radius of curvature of the plano-convex mirror, r is a radial coordinate of the metasurface, and c is a constant.

[0018] If the target working wavelength band is in a visible light wavelength band, the materials of the refractive optical element and the substrate are selected as silica, and the material of the micro-nano structure is selected as one of titanium dioxide, gallium nitride, and silicon nitride; if the target working wavelength band is in a middle infrared wavelength band, the materials of the refractive optical element, the substrate, and the micro-nano structure are selected as silicon; and if the target working wavelength band is in a long-wave infrared wavelength band, the materials of the refractive optical element, the substrate, and the micro-nano structure are selected as germanium.

[0019] The optical device with the composite configuration of the refractive optical element and the metasurface of the present application adopts the composite configuration, cascades the refractive optical element and the metasurface into one body to form a composite optical device, thereby realizing the light weight and integration requirements of the optical system, and realizing optical imaging by using one composite optical device, so that the optical system is small in size and light in weight, and meanwhile, the bottleneck of mutual restriction between aperture and bandwidth is broken through, and the aperture and bandwidth requirements in actual applications can be met. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a structural schematic diagram of an optical device with a composite configuration of a refractive optical element and a metasurface according to an embodiment of the present application.

[0021] Figure 2 is a top view schematic diagram of a metasurface of an embodiment of the present application.

[0022] Figure 3 is a top view schematic diagram of a micro-nano structure unit of a metasurface of an embodiment of the present application.

[0023] Figure 4 is a side view schematic diagram of a micro-nano structure unit of a metasurface of an embodiment of the present application.

[0024] Figure 5A is a relationship diagram of a back intercept of a silicon plano-convex mirror of an optical device with a composite configuration of a refractive optical element and a metasurface of a first embodiment of the present application varying with wavelength.

[0025] Figure 5B is a relationship diagram of a back intercept of a composite optical device of an optical device with a composite configuration of a refractive optical element and a metasurface of a first embodiment of the present application varying with wavelength.

[0026] Figure 6A is a relationship diagram of a back intercept of a silicon plano-convex mirror of an optical device with a composite configuration of a refractive optical element and a metasurface of a second embodiment of the present application varying with wavelength.

[0027] Figure 6BThis is a graph showing the relationship between the back intercept and wavelength of a composite optical device consisting of a refractive optical element and a metasurface composite configuration according to the second embodiment of the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0029] like Figure 1 The image shows an optical device with a refractive optical element and a metasurface composite configuration according to an embodiment of the present invention. Figure 1 As shown, the optical device with the composite configuration of refractive optical element and metasurface is composed of a cascaded refractive optical element 1 and metasurfaces 2 and 3. Metasurfaces 2 and 3 are composed of a substrate 2 and a micro / nano structure 3. The optical device with the composite configuration of refractive optical element and metasurface is configured to receive incident light. The refractive optical element 1 has a plane and a curved surface. The curved surface of the refractive optical element 1 faces the propagation direction of the incident light, while the plane faces away from the propagation direction of the incident light. Metasurfaces 2 and 3 are disposed on one side of the plane of the refractive optical element 1. The metasurfaces are closely bonded to the plane of the refractive optical element 1 through their substrate 2, thus cascading the refractive optical element 1 and the metasurfaces to form a composite optical device. The phase distribution of the refractive optical element at at least one wavelength within the target operating band satisfies the imaging requirements of the optical device. The phase distribution of the metasurface is configured to correct the chromatic aberration of the refractive optical element 1 within the target operating band, thereby enabling the composite optical device formed by the cascaded refractive optical element 1 and the metasurface to achieve broadband achromatic focusing function. This ensures that the phase distribution of electromagnetic waves (i.e., broadband parallel incident light) at different wavelengths within the target operating band, after passing through the optical device with the composite configuration of the refractive optical element and the metasurface of this invention, simultaneously satisfies the imaging requirements of the optical device.

[0030] Two different embodiments of the present invention are given below to illustrate in detail the structure and working principle of the optical device of the present invention.

[0031] In two embodiments of the present invention, the refractive optical element 1 adopts a plano-convex mirror configuration.

[0032] However, in other embodiments, other refractive element configurations are also applicable to the refractive optical element 1, but it is still necessary that one side is a plane and the other side is a curved surface. The curved surface of the refractive optical element 1 faces the direction of propagation of the incident light, while the plane faces away from the direction of propagation of the incident light. Furthermore, the metasurface is in close contact with the plane of the refractive optical element 1 through its substrate 2, so as to cascade with the metasurface. The phase distribution formula of the metasurface under other refractive element configurations needs to be derived based on the surface shape of the refractive element and the function to be achieved by the composite optical device.

[0033] Since the two embodiments of the present application, the refractive optical element 1 adopts a plano-convex mirror configuration, the plano-convex mirror plays a role in focusing parallel light, and the imaging requirement of the optical device refers to the refractive optical element focusing to the focal plane with a preset focal length. Due to the material dispersion of the plano-convex mirror, the focal lengths of different wavelengths of light are different, that is, there is a dispersion problem, and the phase distribution of the metasurface is set to correct the chromatic aberration of the refractive optical element 1 in the target working waveband, so that the composite optical device formed by the cascade of the refractive optical element 1 and the metasurface realizes the broadband achromatic focusing function, that is, the broadband parallel incident light (including incident light of each wavelength in the working waveband) is focused to the focal plane 4 with the preset focal length after passing through the optical device of the refractive optical element and the metasurface composite configuration of the present application.

[0034] Since the phase distribution of the refractive optical element 1 at at least one wavelength in the target working waveband meets the imaging requirement of the optical device as described above, the preset focal length of the refractive optical element 1 can meet the requirement at at least one wavelength in the target working waveband, and specifically can meet the requirement at the center wavelength of the target working waveband, or meet the requirement in the target working waveband deviating from the center wavelength of the target working waveband.

[0035] In the two different embodiments of the present application, the parameters of the two plano-convex mirrors are shown in Table 1.

[0036] Table 1: Parameters of two plano-convex mirrors in embodiments of the present application

[0037] The material of the refractive optical element can be selected from silicon dioxide (quartz), silicon and germanium, the substrate material of the metasurface can be selected from silicon dioxide (quartz), silicon and germanium, and the micro-nano structure material of the metasurface can be selected from titanium dioxide, gallium nitride, silicon nitride, silicon and germanium. The specific material depends on the target working waveband. In the visible light waveband, silicon dioxide (quartz) and titanium dioxide, gallium nitride and silicon nitride have high transmittance; in the mid-infrared waveband, silicon has high transmittance; in the long-wave infrared waveband, germanium has high transmittance.

[0038] Therefore, if the target working waveband is in the visible light waveband, the material of the refractive optical element 1 is selected from silicon dioxide (quartz), the substrate material of the metasurface is selected from silicon dioxide (quartz), and the micro-nano structure material can be selected from titanium dioxide, gallium nitride and silicon nitride.

[0039] If the target working waveband is in the mid-infrared waveband, the material of the refractive optical element 1 is selected from silicon, and the materials of the substrate and the micro-nano structure of the metasurface are selected from silicon.

[0040] If the target working waveband is in the long-wave infrared waveband, the material of the refractive optical element 1 is selected to be germanium, and the substrate and the micro-nano structure material of the metasurface are selected to be germanium. The target working waveband of the two embodiments of the present application is in the mid-infrared waveband, so the materials of the refractive optical element, the substrate of the metasurface, and the micro-nano structure 3 are all selected to be silicon.

[0041] The structure of the metasurface is that the metasurface is composed of a substrate 2 and a micro-nano structure 3. The micro-nano structure 3 of the metasurface is composed of a periodic array of two-dimensionally arranged micro-nano structure units 31. The aperture of the metasurface is set to be consistent with or slightly smaller than the aperture of the refractive optical element 1. In the two embodiments of the present application, the aperture of the metasurface is set to be slightly smaller than the aperture of the refractive optical element, because the refractive optical element in the embodiments is a focusing function, and the light beam has been converged after passing through the refractive optical element, so that the diameter of the light beam is smaller than that when it is incident on the metasurface. The degree of reduction in the diameter of the light beam depends on the geometric parameters of the refractive optical element such as the aperture, focal length, and thickness. The ratio of the aperture of the metasurface to the aperture of the refractive optical element can be 0.7-0.99 times.

[0042] Figure 2 The top view of the metasurface of the embodiments of the present application is shown in FIG. 1. As shown in FIG. 1, the configuration of the periodic array of the micro-nano structure units 31 can be a square lattice array or a hexagonal lattice array. As shown in FIG. 2, the periodic array is a square lattice array (i.e., the center positions of all the micro-nano structure units 31 form a square lattice array). Figure 2 Figure 3 As shown in FIG. 2, the periodic array is a square lattice array (i.e., the center positions of all the micro-nano structure units 31 form a square lattice array). The period U of the periodic array can be 0.2λ to λ (λ is a specified wavelength in the target working waveband). In the periodic array, the micro-nano structure units 31 can be elliptical cylinders or rectangular cylinders. As shown in FIG. 3, in the present embodiment, the configuration of the micro-nano structure units 31 is rectangular cylinders. The micro-nano structure units 31 have various geometric parameters such as height, pointing angle, cross-sectional dimension, etc. The micro-nano structure units 31 have one variable geometric parameter, and the variable geometric parameters of different micro-nano structure units 31 are different, while the remaining geometric parameters are the same. Figure 3 Figure 4 As shown in FIG. 3, in the present embodiment, the configuration of the micro-nano structure units 31 is rectangular cylinders. The micro-nano structure units 31 have various geometric parameters such as height, pointing angle, cross-sectional dimension, etc. The micro-nano structure units 31 have one variable geometric parameter, and the variable geometric parameters of different micro-nano structure units 31 are different, while the remaining geometric parameters are the same.

[0043] ​​According to the geometric phase control principle of the metasurface, the phase control amount of electromagnetic wave passing through the micro-nano structure unit 31 with the same size (i.e. the same height and cross-sectional size) and different pointing angles is irrelevant to the wavelength, and is only related to the pointing angle of the micro-nano structure unit 31, and the phase control amount is twice the pointing angle. According to the dynamic phase control principle of the metasurface, the phase control amount of electromagnetic wave passing through the micro-nano structure unit 31 with different sizes (such as different cross-sectional sizes) is related to the wavelength. In the present application, considering that the metasurface plays a role of correcting the chromatic aberration of the refractive optical element in the composite optical device, if the metasurface itself introduces chromatic aberration, although the chromatic aberration of the refractive optical element 1 is corrected in the composite optical device, the chromatic aberration caused by the metasurface is added, and then the chromatic aberration problem is still not solved, and the wideband achromatic focusing function of the composite optical device is still not achieved, therefore the metasurface itself should not introduce additional dispersion. In order to make the metasurface itself not introduce dispersion, the variable geometric parameter can only be the pointing angle, and the remaining geometric parameters such as the height and cross-sectional size need to be set to be the same. That is, the phase control amount of electromagnetic wave passing through the micro-nano structure unit 31 should be irrelevant to the wavelength, and therefore the geometric parameters such as the height and cross-sectional size of the micro-nano structure unit 31 are set to be unchangeable, and only the pointing angle is set as a variable geometric parameter. The pointing angle of each micro-nano structure unit 31 is determined according to the required phase control amount of electromagnetic wave passing through each micro-nano structure unit 31 and the corresponding relationship between the phase control amount of electromagnetic wave passing through the micro-nano structure unit 31 and the variable geometric parameter of the micro-nano structure unit 31. In the two embodiments of the present application, the variable geometric parameter of the micro-nano structure unit 31 is the pointing angle, and each micro-nano structure unit has the same size (i.e. the same height and cross-sectional size) and different pointing angles, wherein the height H can be 0.5λ to 1.5λ, the cross section of the micro-nano structure unit 31 is rectangular, the cross-sectional size L (the long side of the rectangle) and W (the short side of the rectangle) can be 0.1U to 0.9U (U is the period of the periodic array), and the pointing angle α can be 0 to π. The pointing angle α of each micro-nano structure unit 31 is determined according to the required phase control amount of electromagnetic wave passing through each micro-nano structure unit 31 and the corresponding relationship between the phase control amount of electromagnetic wave passing through the micro-nano structure unit 31 and the pointing angle of the micro-nano structure unit 31, and the phase control amount is twice the pointing angle of the micro-nano structure unit 31. The phase control amount of electromagnetic wave passing through each micro-nano structure unit 31 should satisfy the phase distribution of the metasurface described above.

[0044] In the embodiment, the refractive optical element adopts a plano-convex mirror configuration, and the design method of the super surface is as follows: in the composite optical device, the refractive optical element causes the focal lengths of electromagnetic waves of different wavelengths in the working waveband to be different due to material dispersion, the chromatic aberration is corrected through the super surface, and the composite optical device formed by cascading the two has the same focal length of electromagnetic waves of each wavelength in the working waveband, that is, the broadband achromatic focusing function is realized.

[0045]

[0046] The refractive optical element in the embodiment of the application adopts silicon material, according to the measured data of the refractive index of silicon, the Cauchy dispersion formula is fitted, and in the case of setting the wavelength unit as μm, the Cauchy dispersion coefficients of silicon in the mid-infrared waveband obtained by fitting are as follows: the first Cauchy dispersion coefficient A = 3.4164, and the second Cauchy dispersion coefficient B = 0.1441.

[0047] The refractive optical element adopts a plano-convex mirror configuration, in order to correct chromatic aberration (that is, in order to make the phase distribution of electromagnetic waves of different wavelengths in the target working waveband after passing through the optical device meet the imaging requirements of the optical device at the same time), the phase distribution of the super surface that needs to be met is as follows:

[0048]

[0049] Wherein, B is the second Cauchy dispersion coefficient, λ0 is the center wavelength of the target working waveband, R is the curvature radius of the plano-convex mirror, r is the radial coordinate of the super surface (the distance from any position on the super surface to the center of the super surface), and c is a constant. Wherein, the center wavelength of the target working waveband is the average value of the minimum wavelength λ min and the maximum wavelength λ max of the working waveband, that is, λ0 = (λ min + λ max ) / 2.

[0050] At different wavelengths, the phase distribution that the super surface needs to meet is the same. Therefore, by designing the pointing angle α of each micro-nano structure unit of the super surface, the phase regulation amount of electromagnetic waves after passing through each micro-nano structure unit meets the above phase distribution, so that the super surface can play a role in correcting chromatic aberration through its phase distribution.

[0051] In the first embodiment of the present application, the refractive optical element is the first plano-convex lens in Table 1, which is a ready-made silicon plano-convex lens product from Thorlabs Company, with an aperture of 25.4 mm, a focal length of 50.0 mm at a wavelength of 4.0 μm, a back intercept of 48.8 mm at a wavelength of 4.0 μm, a radius of curvature of 121.3 mm, and a material of silicon. Since the plano-convex lens acts as a converging lens, the aperture of the metasurface is set to be slightly smaller than the aperture of the plano-convex lens, i.e., 20 mm. The target working wavelength range of the optical device is 3.9-4.7 μm, and the center wavelength of the target working wavelength range is 4.3 μm. The required phase distribution of the metasurface is obtained by substituting the Cauchy dispersion coefficient of silicon, the center wavelength of the composite optical device, and the radius of curvature of the plano-convex lens into the above formula of the phase distribution of the metasurface. The broadband achromatic focusing function of the composite optical device is verified by ray tracing simulation.

[0052] Figure 5A and Figure 5B is a graph of the change of the back intercept of the silicon plano-convex lens of the first embodiment of the present application with wavelength and a graph of the change of the back intercept of the composite optical device with wavelength. The back intercept is the distance from the last surface of the optical device to the focal plane. The greater the change of the back intercept with wavelength, the greater the chromatic aberration of the optical device, and the smaller the change of the back intercept with wavelength, the smaller the chromatic aberration of the optical device. The change of the back intercept of the silicon plano-convex lens with wavelength in the wavelength range of 3.9-4.7 μm (with a wavelength interval of 0.2 μm) is shown in Figure 5A , and the back intercept difference (or focal length difference) is 0.061 mm. The change of the back intercept of the composite optical device with wavelength in the wavelength range of 3.9-4.7 μm (with a wavelength interval of 0.2 μm) is shown in Figure 5B , and the back intercept difference (focal length difference) is only 0.005 mm, which is only 1 / 12 of the back intercept difference (focal length difference) of the silicon plano-convex lens. This result verifies the chromatic aberration correction effect of the metasurface in the composite optical device and also verifies the broadband achromatic focusing function of the composite optical device.

[0053] In the second embodiment of the present application, the refractive optical element is the second plano-convex lens in Table 1, which is a ready-made silicon plano-convex lens product from Thorlabs Company, with an aperture of 25.4 mm, a focal length of 100.0 mm at a wavelength of 4.0 μm, a back intercept of 98.8 mm at a wavelength of 4.0 μm, a radius of curvature of 242.5 mm, and a material of silicon. Since the plano-convex lens acts as a converging lens, the aperture of the metasurface is set to be slightly smaller than the aperture of the plano-convex lens, i.e., 20 mm. The working wavelength range of the composite optical device is 3.9-4.7 μm, and the center wavelength is 4.3 μm. The required phase distribution of the metasurface is obtained by substituting the Cauchy dispersion coefficient of silicon, the center wavelength of the composite optical device, and the radius of curvature of the plano-convex lens into the above formula of the phase distribution of the metasurface. The broadband achromatic focusing function of the composite optical device is verified by ray tracing simulation.

[0054] Figure 6A and Figure 6B is a graph showing the variation of back focal length of the silicon plano-convex lens and the variation of back focal length of the composite optical device with wavelength according to the second embodiment of the present application. The variation of back focal length of the silicon plano-convex lens in the wavelength range of 3.9-4.7 μm (with a wavelength interval of 0.2 μm) is shown in FIG. 4, and the back focal length difference (or focal length difference) is 0.121 mm. The variation of back focal length of the composite optical device in the wavelength range of 3.9-4.7 μm (with a wavelength interval of 0.2 μm) is shown in FIG. 5, and the back focal length difference (focal length difference) is only 0.01 mm, which is only 1 / 12 of the back focal length difference (focal length difference) of the silicon plano-convex lens. This result again verifies the chromatic aberration correction effect of the metasurface in the composite optical device, and again verifies the wideband achromatic focusing function of the composite optical device. Figure 6A Figure 6B Since the focal length of the refractive optical element 1 in both embodiments of the present application is 4.0 μm, the focal length and back focal length given by the two silicon plano-convex lens products of Thorlabs Company are for the center wavelength of 4.0 μm in the mid-wave infrared wavelength range of 3-5 μm. In the present application, when the phase distribution of the metasurface is used to correct chromatic aberration, the center wavelength of 4.3 μm of the target working wavelength range is taken as λ0 in the phase distribution formula of the metasurface, and it does not need to be set to the wavelength of 4.0 μm given in the product parameters of the silicon plano-convex lens (that is, the preset focal length of the refractive optical element 1 is a fixed value, and the working wavelength corresponding to the preset focal length of the refractive optical element 1 itself can deviate from the center wavelength of the target working wavelength range to meet the imaging requirements of the optical device). After adding the metasurface, the focal length or back focal length of the composite optical device at each wavelength is different from the focal length or back focal length of the single refractive optical element at the corresponding wavelength, and the effect of adding the metasurface is to significantly reduce the variation of the focal length or back focal length with wavelength.

[0055] The structure of the refractive optical element 1 can be an aperture of 10 mm to 15 cm, a focal length of 10 mm to 100 cm, and a surface shape of a spherical surface or an aspherical surface. The refractive optical element 1 in both embodiments of the present application adopts a plano-convex lens configuration, with a curved surface in front and a flat surface in back, and the curved surface is a spherical surface.

[0056] The structure of the refractive optical element 1 can be an aperture of 10 mm to 15 cm, a focal length of 10 mm to 100 cm, and a surface shape of a spherical surface or an aspherical surface. The refractive optical element 1 in both embodiments of the present application adopts a plano-convex lens configuration, with a curved surface in front and a flat surface in back, and the curved surface is a spherical surface.

[0057] ​The above merely describes preferred embodiments of the present application, and is not intended to limit the scope of the present application. The above-described embodiments of the present application can be variously changed. That is, simple, equivalent changes and modifications made in accordance with the content of the claims and the specification of the present application are intended to fall within the scope of the present application. The present application is not limited by the above-described embodiments.

Claims

1. An optical device of a refractive optical element and metasurface hybrid configuration, characterized in that, The optical device of the refractive optical element and metasurface composite configuration is composed of a refractive optical element and a metasurface, a phase distribution of the refractive optical element at at least one wavelength in a target working waveband meets the imaging requirement of the optical device, and a phase distribution of the metasurface is set to correct chromatic aberration of the refractive optical element in the target working waveband, so that the phase distribution of electromagnetic waves at different wavelengths in the target working waveband after passing through the optical device meets the imaging requirement of the optical device at the same time. The refractive optical element has a focusing function, and a ratio of the metasurface to an aperture of the refractive optical element is 0.7-0.

99. The refractive optical element adopts a plano-convex mirror configuration, and the imaging requirement of the optical device means that the refractive optical element focuses to a focal plane with a preset focal length. The phase distribution of the metasurface is: wherein B is a second Cauchy dispersion coefficient, λ0 is a center wavelength of the target working waveband, R is a curvature radius of the plano-convex mirror, r is a radial coordinate of the metasurface, and c is a constant.

2. The optical device of claim 1, wherein the refractive optical element is a lens. The metasurface is composed of a substrate and a micro-nano structure, the micro-nano structure is composed of a periodic array of two-dimensionally arranged micro-nano structure units, the micro-nano structure units have variable pointing angles, the pointing angles of different micro-nano structure units are different, and the remaining geometric parameters are the same. The pointing angles of the micro-nano structure units are determined according to the required phase regulation amount of the electromagnetic waves passing through the micro-nano structure units and the corresponding relationship between the phase regulation amount of the electromagnetic waves passing through the micro-nano structure units and the pointing angles of the micro-nano structure units; the phase regulation amount of the electromagnetic waves passing through the micro-nano structure units satisfies the phase distribution of the metasurface.

3. The optical device of claim 2, wherein the refractive optical element is a lens. The periodic array is a square lattice array or a hexagonal lattice array, a period U of the periodic array is 0.2λ to λ, and the micro-nano structure units are elliptical cylinders or rectangular columns, λ being a specified wavelength in the target working waveband.

4. The optical device of claim 3, wherein the refractive optical element is a lens. The pointing angles of the micro-nano structure units are between 0 and π, and a height H of the micro-nano structure units is 0.5λ to 1.5λ.

5. The optical device of claim 3, wherein the refractive optical element is a lens. The micro-nano structure units are rectangular columns, a rectangular long side L and a rectangular short side W are 0.1U to 0.9U, and U is a period of the periodic array.

6. The optical device of claim 2, wherein the refractive optical element is a lens. One face of the refractive optical element is a plane, and the other face is a curved surface, the curved surface of the refractive optical element faces the propagation direction of incident light, and the plane faces away from the propagation direction of incident light, and the metasurface is closely attached to the plane of the refractive optical element through the substrate thereof.

7. The optical device of claim 2, wherein the refractive optical element is a lens. If the target working waveband is in the visible light waveband, the materials of the refractive optical element and the substrate are selected from one of silicon dioxide, titanium dioxide, gallium nitride, and silicon nitride, and the material of the micro-nano structure is selected from one of titanium dioxide, gallium nitride, and silicon nitride; If the target working waveband is in the mid-infrared waveband, the materials of the refractive optical element, the substrate, and the micro-nano structure are selected from silicon; If the target working waveband is in the long-wave infrared waveband, the materials of the refractive optical element, the substrate, and the micro-nano structure are selected from germanium.

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